It is known that plasmapheresis consists in removing blood from a donor or from a patient to introduce it in an extracorporeal circuit which comprises a filter in which a liquid fraction, called plasma, is separated from the blood mass which contains the cell fraction which is then reintroduced into the donor or patient; the plasma is then kept, in the case of removal from a donor, or eliminated if it is taken from a patient in order to replace it.
In proceeding with a single-needle extracorporeal circuit, the process includes a series of cycles, each of which has a blood withdrawal step and a subsequent step for the reintroduction of the fraction which remains after plasma separation, which ends when the plasma collection reaches the required amount.
In the extracorporeal circuits more commonly comprised within the known devices and methods, the filter in which the plasma is separated from the blood has a blood circuit connected at one end to a line provided with a pump connected to a single needle and at the other end to a line which leads into a blood collection reservoir, and is furthermore provided with a plasma container connected by a line to a plasma collection bag.
The extracorporeal circuit thus configured allows a plasmapheresis process in which the plasma is separated from the blood exclusively during the steps of removal of the blood from the patient or donor, whereas during the subsequent reinfusion steps no plasma separation is performed and the plasma container is simply clamped to prevent pumping plasma or other liquids which are present in the system.
Such processes therefore have the disadvantage of one active step out of two for each of the cycles, only one active step out of two, and of consequently entailing long cycle times, which are particularly unpleasant if the plasmapheresis relates to a donor.
The known devices also include a type of extracorporeal circuit in which there is a line for recirculating part of the blood through a filter during reinfusion, but with this method there is the risk of not operating within the optimum range of pressures of the fluids present in the system, resulting in a decrease in the efficiency of the system. The larger amount of blood not reinfused to the patient or donor leads to a decrease in the amount of fresh blood which can be drawn during a subsequent step.
The aim of the present invention is thus to provide a single-needle extracorporeal plasmapheresis circuit which, by operating with the maximum possible efficiency, allows a drastic reduction in the time required for carrying out the plasmapheresis process.